The term “food allergy” refers to adverse immunologic reactions to food. Food allergy is typically mediated by IgE antibodies directed to a specific food protein, but other immunologic mechanisms can also play a role in this phenomena. The primary target organs for food allergy reactions are the skin, the gastrointestinal tract, and the respiratory system.
Both acute reactions (hives and anaphylaxis) and chronic diseases (asthma, atopic dermatitis and gastrointestinal disorders) may be caused or exacerbated by food allergy.
Foods commonly causing these reactions in children are: milk, eggs, peanuts, soy, wheat, tree-nuts, fish and shellfish. In adults, the most common foods are: peanuts, tree-nuts, shellfish and fruit.
Several specific tests have been developed for the evaluation of IgE-mediated food allergies, in order to identify or exclude responsible foods.
One method of determining the presence of specific IgE antibodies to various allergens, among them food allergens is the “prick-puncture skin testing”. While the patient is not taking antihistamines, a device such as a bifurcated needle or a lancet is used to puncture the skin through glycinerated extract of a food and also through appropriate positive (histamine) and negative (saline-glycerine) control substances. A local “wheal-and-flare” response indicates the presence of food-specific IgE antibodies, wherein a wheal having a diameter of more than 3 mm is typically considered as indicating a positive response.
Prick skin tests are most valuable when they are negative, since the negative predicted value of this test is relatively high (estimated to be above 95% for IgE mediated reactions). However, the positive predicted value of these tests for such IgE mediated reactions is only on an order of 50%. Thus a positive skin test in isolation cannot be considered as a proof of clinically relevant hypersensitivity. Another disadvantage of the prick skin test is that many patients are reluctant to be repeatedly pricked for identifying the responsible food. Furthermore, the test is quite time consuming, typically requiring several test sessions at the practitioner's office, each one for testing several suspected foods.
In vitro blood testing for specific IgE (Radioallergosorbent tests (RAST)) is another option for diagnosing food allergies. As with skin tests, a negative result in RAST testing is relatively reliable in ruling out an IgE-mediated reaction to a particular food, however a positive result has low positive predicted value. Another disadvantage of RAST is that it is an invasive test requiring obtaining a blood specimen from the patient and sending it to a laboratory to be analyzed, which analysis is quite expensive. Furthermore, since the test cannot be carried out in the practitioner's office the results are very often delayed.
Double-blind placebo-controlled food challengers are another option for diagnosis of food allergies. According to this option, patients avoid the suspected food for at least two weeks, while discontinuing antihistamine therapy. Other allergy medication, such as anti-asthma medication are reduced as much as possible. Then graded doses of either challenge food or placebo food are administered to the patient. The food is hidden under another food or is taken as capsules as it is consumed without the patient knowing its nature. Medical supervision and immediate access to emergency medications including antihistamines, steroids and inhaled beta antagonists, and equipment for cardiopulmonary resuscitation are required since the allergic reactions can be severe and may even include shock. It is clear that, while such a labor intensive and potentially dangerous procedures can detect acute reaction to the food allergies, they can not detect chronic reaction and in no way can be considered as standard procedure for determining allergies to foods.
There have been a number of studies indicating the problematic high false negative results of various food allergies when blood and skin tests are performed (Thompson et al., The Lancet, Jan. 22, (1983)).
Further research involved testing the presence of antibodies in mucosal secretions (such as feces) in connection with food allergy testing. It was found that a higher percentage of children with allergy feature IgE in feces as compared to the rare occurrence of IgE immunoglobulin in extracts of feces from healthy children (Kolmannskog, Int. Archs Allergy Applic. Immunol. 76:133-137, (1985)). The hypothesis was that the IgE may at least in part have been produced locally in the gut mucosa. These findings were supported by the findings that increase Copro IgE (in faecal extracts) are a specific consequence of the local immune response to food allergy simulation in gut mucosa (Sasai et al. in Allergy, 47:594-598 (1992)).
Self et al. (JAMA, March 31, 207:13, 2393 (1969)) demonstrated stool precipitants against dietary antigens being in children suspected of having various food allergies. These studies indicate the initiation of antibodies to specific food antigens, which could be detected in the stool of the allergic children.
The studies by Self et al. further suggested that the precipitated antibodies are contained in the immunoglobulin A (IgA) fraction of the intestinal secretion, which finding is also in accordance with the fact that most plasma cells of the intestines contain IgA and, unlike serum, intestinal secretions contain large amounts of IgA and lesser amounts of the other immunoglobulin.
The traditional model of clinical laboratory tests has been that a physician orders a test, a biological specimen such as blood, urine, throat culture, etc. is obtained and sent to a clinical laboratory, and days or weeks later the laboratory result is sent to the physician. The patient then returns to the physician's office to learn result and received advice concerning his or her medical condition. While this model is appropriate for many complicated physiological conditions, there are many other physiological situations where the patient is, or can easily be, well equipped to understand the results of a lab test, has an interest or need to know the result immediately, and is capable of performing the test by himself, and understanding the test results.
Thus, over the past decades home tests for pregnancy have become very popular. Home tests for glucose for diabetic patients have also become very popular. Other tests, such as tests for cholesterol levels, are beginning to gain wide popularity. Still other tests, such as those for day of ovulation are not yet widely known, but are gaining market acceptance.
Thus, a substantial market exists for home diagnostic tests and there is constant need to develop additional home tests for further physiological conditions.